Efflorescence is a calcium or alkaline salt which forms as a blotchy, powdery or crystalline deposit on the surface of masonry and concrete products. It is due to moisture entering through the masonry, combining with the calcium hydroxide in the cement, and bringing the hydroxide to the surface in a solution which forms crystals when it combines with the carbon dioxide in the air. It is usually white but efflorescence may be yellow, green or brown.
Efflorescence is generally caused by salt-bearing compounds entering the masonry material. Although new, fresh bricks do not generally contain significant amounts of soluble salts, mortar and concrete do have relatively high soluble salt contents. Ground waters that are naturally salt-bearing can also seep into the masonry, as well as other sources of water, such as rain, lawn sprinklers, leaky pipes and others. The amount of efflorescence that occurs is related, inter alia, to the amount of water in the bricks, and their drying time. The more water in the bricks, and the longer it is there, the more chance salts will have to dissolve in it and be brought to the surface as the bricks dry out.
In the prior art, attempts to control efflorescence include waterproof coatings applied to the surface of the masonry units. The application of such coatings is not always effective and is costly in terms of labor, coating materials and time. One of the most common methods is to simply “give up” and brush off the efflorescence deposits with a stiff dry bristle brush after the wall has dried out.
U.S. Pat. No. 6,537,366 to Supplee, Sr. describes a composition for coloring concrete, which includes a hydrophobic efflorescence control agent, such as a stearate-containing compound. Supplee, Sr. states that although stearate-containing compounds (e.g., calcium stearate, zinc stearate, aluminum stearate, among other suitable compounds of stearic acid, salts and derivatives thereof, and mixtures thereof) may be used to minimize or eliminate efflorescence, they are also known to adversely affect the durability of concrete. Concrete durability is a function of the totality of the polymerization of the cementitious materials in a mix. Because efflorescence control agents hinder polymerization, use of efflorescence control agents yield a weaker polymer structure and hence a less durable concrete.
Supplee, Sr. describes a concrete admixture composition that includes about 0.1% by weight to about 85% by weight of a hydrophobic efflorescence control agent; about 0.5% by weight to about 75% by weight of a particulated polymer, the particulated polymer having particle sizes of about 50 angstroms to about 7,000 angstroms; and about 0.001% by weight to about 80% by weight of a colorant in an aqueous dispersion of the total weight of the composition. The composition also includes a property enhancing additive selected from the group consisting of plasticizers, surfactants, rheology modifiers, biological control agents, and a mixture thereof.
The efflorescence control agent may be one of the stearate-containing compounds mentioned above, or may be selected from the group consisting of tall oil fatty acids, vegetable and animal fats, emulsions based on white grease, silicone compounds, siliconates, and siloxanes, waxes, wax emulsions, soaps and fatty acids, vegetable oils and emulsions, petroleum residues, including mineral oil, paraffin, and bitumens, various pozzolanics, including fly ash, blast furnace slag, diatomaceous earth, inert fillers, including talc, bentonite, and siliceous powders, and a mixture thereof. The particulated polymer is selected from the group consisting of styrene-based polymers and copolymers, acrylic-based polymers and copolymers, polyvinyl acetates, polyepoxides, polyurethanes, butadiene rubbers, and a mixture thereof.